EMS differs from TENS in that EMS is designed to stimulate motor neurons while TENS is designed to stimulate sensory neurons. As such, EMS is used to create muscular contractions and subsequent relaxations that are effective for a variety of reasons from strength to rehab. TENS stimulates sensory nerves which results in decreased pain. TENS treatment can also stimulate endorphin release.
One vital aspect of electrotherapy is the effect of swelling. Using a passive or low intensity exercise to keep the fluid moving after heavy sessions can help remove cellular debris. One elite athlete that I know of uses microcurrent during naps post training for up to two hours at time. Research on animals has been very impressive using this technique but only ulcers and slow healing wounds seem to be aided by such measures.